Overview & Objective(s): Determine relative abundance, distribution, movements, and habitat use of manatees associated with coastal waters and rivers from Marco Island through Whitewater Bay. Identify resources critical to manatees in the region, including distribution and abundance of submerged aquatic vegetation, freshwater drinking sites, and winter refugia. Develop an individual-based ATLSS model to predict manatee response to changes in hydrology achieved by the Picayune Strand Restoration Project specifically and more broadly by the Comprehensive Everglades Restoration Plan. Additional information on population trend, distribution, and habitat use, coupled with models of hydrology, bathymetry, aquatic vegetation, and salinity, will allow development of a population-level model capable of predicting manatee response to future changes. The ATLSS model requires a hydrology model for the rivers and estuaries of the Ten Thousand Islands region and this hydrology model is not currently available. This integrated manatee/hydrology modeling effort can provide invaluable information as a small-scale test case for understanding and predicting how restoration efforts in the Everglades will affect manatees.

Status:PES funding is scheduled to end in FY05. This study has provided insights into pre-restoration conditions and establishes a baseline for manatees and estuaries associated with the TTI. Findings have also identified relevant habitat characteristics for additional research and helped restoration/recovery agencies focus attention on appropriate management actions. An extension of an Everglades hydrology model into the TTI is needed in order to complete the ATLSS model. Proposals for integrated studies to extend hydrology models into the TTI are pending. This model effort would benefit the completion of this ATLSS product, and numerous other studies focused on the wetlands and estuaries in this region.

Each manatee project task addresses a number of USGS project tasks related to hydrology, habitats and species, ecological indicators, and threatened and endangered species. Because the manatee is a federally listed species, our work supports a variety of needs identified by the DOI for listed species.

Key Findings:

Satellite-based Argos transmitters were used to track movements of 33 manatees between June 2000 and August 2004 for 8599 tag-days. We tracked 18 manatees with GPS tags for more than 1,800 tracking days, obtaining approximately 85,000 high precision fixes at 15-30 minute intervals. Several lines of evidence based on the telemetry data indicate that reliable assess to freshwater for drinking is a critical habitat requirement for manatees. First, all tracked manatees made frequent, long-distance movements alternating between offshore seagrass beds and various inshore access points for freshwater (e.g. rivers, tidal creeks, and canals) at regular intervals ranging from 2-8 days throughout the year. Second, during the dry season most manatees visited only one or a few freshwater assess points that are known to be reliable sources of freshwater, compared to the wet season when many more inshore sites were assessed and are known to be seasonally reliable sources of freshwater. In response to the increased availability of freshwater sites during the wet season, manatees shifted their homeranges to different areas compared to the dry season. Third, manatees spend significantly more time within inshore areas during the dry season compared to the wet season. Because restoration activities are expected to change the timing and quantity of freshwater inflow to rivers and canals in the study area, we expect manatee movement patterns to change in response to the changing availability of freshwater.

Due to the absence of warm springs and artificial sources of warm water, manatees within TTI/ENP are subject to cold stress and cold-related mortality during the winter at a higher rate than many areas further north. Telemetry data indicates that they exhibit complex behavioral responses to cold weather, including: 1) migrating south into Whitewater Bay, 2) bottom resting in warm water layers trapped in deeper sections of basins, canals, and rivers, and 3) sheltering in shallow bays that heat up rapidly following the passage of cold fronts and return of warmer temperatures. An on-going, complementary study by the USGS/Sirenia Project to characterize winter refugia for manatees in the northwestern Everglades region will help address how restoration activities might influence the thermal regimes of manatee over-wintering sites.

Aerial surveys and telemetry data show similar seasonal patterns in manatee distribution, with much greater use of inland areas during the winter at a few aggregation sites, and much greater use of offshore areas during the summer, when manatees are widely disbursed throughout the study area. Minimum counts of manatees during aerial surveys of the Ten Thousand Islands exceeded 230 individuals, demonstrating the importance of this area to the statewide population.

Additional research efforts on manatee use of the Everglades have resulted from this study. In addition to documenting detailed habitat use through GPS-based radio tracking and parameterizing the individual-based ATLSS model, these findings are being correlated with aerial survey data for refining population assessment models. Other focused research efforts are revealing manatee over-wintering strategies and providing insights in manatee use in the southern ENP. Findings from these associated efforts have provided insights for manatee recovery and management in a poorly understood but important region for manatees.